In chemical and biomedical research and development, it is common to manipulate large numbers (e.g., thousands) of fluid containers which must be readily and automatably opened and closed, and yet must also be stored for months or years. The need to open and close the containers readily tends to induce the use of relatively poorly sealed containers, whereas the desire to store the containers for months or years tends to make it desirable to achieve tight sealing, for example to avoid evaporation loss and contamination from the outside.
The fluid containers used in chemical and biomedical research are subject to substantial chemical compatibility constraints, for example that they should not be made of materials which would be attacked by the solvents which they are designed to hold. Such constraints will also apply to the closures of such fluid containers. Adhesives are generally not preferred for closure of such fluid containers because of concerns about contamination and nonuniformity arising from adhesive residue left over from one closure to the next. Adhesives are nonetheless in widespread use.
Examples of fluid containers widely used in chemical and biomedical research and development are well plates and micro tubes. Well plates are commonly used which have 96, 384, and 1536 wells, although other numbers of wells are also in use. The dimensions and other characteristics of well plates have been standardized by the Society for Biomolecular Screening. A common size of well plate is 127.76 by 85.48 by 14.35 mm. Well plates are commonly designed to be stacked on top of each other in storage. Microtubes are commonly used in racks of 96 or 384. These racks of microtubes conform to dimensions similar to the length and width of well plates so they can be handled by similar robotic and automation equipment.
For well plates, a wide variety of lids have been developed. An example of a well plate lid of the prior art is described in U.S. Patent Application Publication No. 2003/0108450. That well plate lid uses the weight of the lid to provide the force which holds the lid to the well plate. The lid is stated to weigh 400 g preferably. A compliant sealing member, preferably of silicone rubber, forms part of the lid and is pressed against the well plate.
A commercially available lid for well plates is the SealTite lid from TekCel, Inc. (Hopkinton, Mass.). The SealTite lid has a metal spring/clamp structure to form a better seal than would be possible if the weight of the lid were the only force holding the lid to the well plate. The use of force as provided, for example, by a spring/clamp may give rise to difficulties in automation of the handling of well plates with lids. See in this regard the TekCel poster at http://lab-robotics.org/Presentations/Posters/Poster2038.pdf.
There have also been efforts in the art to adapt to evaporation losses. In particular, in some cases the outer wells of a well plate are not used to hold fluids of interest but instead are filled with a volume of the solvent in which those fluids are stored. This solvent in the outer wells has been observed to reduce the rate at which the solvent in the inner wells evaporates. The outer wells are sometimes referred to as “moat wells” when so used.
An alternative means to adapt to evaporation losses is to periodically audit the fluid levels in the reservoirs of the container and to add solvent to those reservoirs as needed. United States Patent Application Publication No. 2003/0150257 describes a convenient automatable way of carrying out the auditing by means of focused acoustic energy.
Cost considerations make it preferable for the containers and their closures to be manufactured by means of molding or similarly economical processes, with limited or no machining. Typical molding processes such as injection molding result in different reservoirs within a container, such as wells in a well plate, being different from each other. For example, there may be a small overall bending or “bow” across a well plate. Such bow is expected, for example, when polymer is injected into the mold at a single point—the “gate”—which is located in or near the center of a substantially flat part such as a well plate. Such processes may also result in there being dimensional differences between different supposedly identical containers or closures manufactured from the same molds or molds intended to be identical. In addition, because containers and their closures may be manufactured separately, by different companies, there may be dimensional mismatches in both containers and closures which result in imperfections in intended mating of containers and closures.
It is often desired to maintain well plates for periods of months. In such situations, it is desired to be certain that the well plates can last for a known time without need for inspection or replenishment. If even only one well of the well plate loses solvent too quickly, this desirable certainty is not achieved.
There is therefore a need in the art to adapt to the evaporation losses caused by less than perfect seals which are used in order to facilitate the automated opening and closing of containers which hold small quantities of fluid.